1. Field of the Invention
The invention relates to a device having one or more manually controlled functions, such as a motor vehicle, in which one or more feedback loops feed back a signal or signals, representing the controlled functions, to one or more comparators, in which the control order is compared to the function signal and a differential signal formed to control the function in question.
2. Prior Art
An important number of theoretical and experimental studies have described the optimum dynamic behaviour of a vehicle, studies based on the actual moving vehicle technology, with propulsion by wheels, steering by wheel inclination, braking through wheels, etc.
Dynamic conditions of this behaviour, are becoming specifications for the car makers, for the tomorrow's car: as for example, braking performances, steady state, yaw response, transient yaw response, returnability, lateral acceleration, breakaway, directional stability, etc. The corresponding minimum safety limits have been established in the "American Proposal Limits for ESV-Specifications" (U.S.--DOT).
It seems reasonable to assume, at a first glance, that with international accepted safety rules for the car, safety would be so much improved, that accident rates and death toll could show a significant decrease. Unfortunately, reality is different: some recent surveys show that more than 90% of the direct causes of accidents, and more than 70% of the indirect causes, are not to be attributed to the car, but to the driver, and his reactions at the controls of the vehicle, in connection with the road conditions. (Mr. Sherigu International Conference on E.S.V.--October 1971).
So, there is no doubt that the "ultimate" safe transportation must not take in account only the vehicle and the road, but also the behaviour of the driver. Driver behaviour, driver reactions in given situations, assessment of driving skill, etc. have been analysed and the results have been published, especially in the recent past.
So it was known that even simple motor tasks, have "learning curves" on extended periods, that is to say improvement replaces lack of performance, i.e. driving risks and potential danger towards others. (O. G. Edholm, The Biology of Work, McGraw-Hill, 1967). In general, skill at any task increases with experience and, in driving, is related to smoothness of control and coordination of the various controls. In the last ten years, several researchers have attempted to use instrumented cars, to assess a driver's performance. Studies done by Greenshields and Platt suggest that a more skilful driver uses fewer control motions (brake, accelerator and steering) and that drivers can be separated into groups of differency experience and ability on the basis of the pattern of their control movements. (B. Greenshields, "Driving Behavior and Traffic Accidents", International Road Safety Congress Proceedings, 1962; and N. Greenshields and F. Platt, "Development of a Method of Predicting High-Accident and High Violation Drivers, "Journal of Applied Psychology, Vol. 51, no. 3, 1967). Safren et al conducted similar experiments, but used a closed track with no other traffic and each subject did several runs, as opposed to only one. They found that patterns of correlation between the various measures differed between experienced and inexperienced drivers. (M. Safren, S. Cohen and L. Schlesinger, "The Drivometer as a Measure of Skill," Journal of Safety, March, 1970). Wooler (1972) used consistency of behaviour of the driver within the traffic stream (passing movements, speed, running time) rather than control movements to rate drivers. (J. Wooler, "The Measurement of Driver Performance," Ergonomics, 15(1), 1972).
Some work has also been done, mainly by Mc. Lean and Hoffman on the stimuli which cause particular patterns of control movements (mainly steering) to be made. (J. McLean and E. Hoffman, "Analysis of Drivers' Control Movements," Human Factors, 13(5), 1971, J. McLean and E. Hoffman, "The Effects of Lane Width on Driver Steering Control and Performance," Austrailian Road Research Board Sixth Conference Proceedings, 1972; and J. McLean and E. Hoffman, "Steering Reversals as a Measure of Driver Performance and Steering Task Difficulty," unpublished). It has been shown that, under normal circumstances, steering is mainly stimulated by the changing heading rate of the car. Under difficult circumstances, the lateral movement of the car, with respect to the edge of the lane may also stimulate steering responses.
Very recently Smiley used statistical techniques to analyse repetitive experiments, and to study correlations in the driver's behaviour. (A. M. Smiley, "The Measurement of Driver Performance," Canada National Aeronautical Establishment, Report LTR-ST, 63B, Sept. 11, 1973.).